Recent years have seen advancement in development of materials utilizing a wide variety of coating techniques. Coating techniques for thin layers on thickness levels of several micrometers to several tens of nanometers in particular are necessary for optical films, graphic arts, photolithography and the like, and the coating accuracy required therein is also being increased, e.g., as the coating layer is reduced in thickness, the substrate is upsized and the coating is speeded up. In manufacturing optical films in particular, the film thickness control is a very important point because it has a decisive influence on optical performance, so there is a growing demand for techniques that permit achievement of speedups in coating operations while assuring continued accuracy.
For the purpose of preventing a contrast drop and degradation of image viewability due to reflections of outside light in image display devices, such as a cathode-ray tube (CRT) display device, a plasma display panel (PDP), an electroluminescent display (ELD) and a liquid crystal display (LCD), an antireflective film is generally placed at the outermost surface of each display so as to reduce the reflectance through utilization of the principle of optical interference.
As those display devices, especially display devices having thinner depth dimensions and wider display areas than traditional CRTs, have proliferated in recent years, demand for display devices with higher definition and higher quality has come to grow. With this trend, uniformity of surface conditions has urgently been required for antireflective films. The term “uniformity of surface conditions” as used herein means that neither variations in optical performance, notably antireflection performance, nor variations in physical properties as film, notably a scratch-resistant property, are present in the overall display area.
As a method of manufacturing antireflective film, the inorganic vapor deposition method as described in Patent Document 1 can be cited. In this document, the silicon oxide film formed using a CVD method is disclosed as an antiglare antireflective film having excellent gas-barrier, antiglare and anti-reflection properties. In point of high-volume production capability, however, a method of manufacturing antireflective film by all-wet coating has an advantage.
Although an all-wet coating method using a solvent is highly advantageous from the viewpoint of productivity, it is very difficult to perform drying of the solvent right after the coating as dried conditions are kept uniform, so unevenness in surface conditions tend to develop. The expression “unevenness in surface conditions” as used herein is intended to include unevenness of drying which results from a difference in solvent drying speeds, unevenness of airing as unevenness in thickness caused by drying air variations, and unevenness of coating which occurs in a coating division. For further increasing the productivity in all-wet coating, the speeding up of a coating operation is an essential technique. However, a simple increase in coating speed involves relatively increasing the velocity of drying air and produces an effect of entrained wind resulting from high-speed transport of a support; as a result, the unevenness of airing becomes worse. In addition, the coating division becomes more unstable, so the unevenness of coating becomes worse in many cases. Accordingly, it has so far been impossible to much increase the coating speed with the intention of obtaining antireflective film reduced in variations of optical performance and physical film properties.
It is known that enhancement of leveling quality is effective in reducing the unevenness which develops under drying. As a measure taken to enhance the leveling quality, addition of surfactants to coating compositions has been put forth. This measure is based on a mechanism that, when a surfactant is added to a coating composition, the coating composition is reduced in surface tension to result in improvement in its ability to wet a material to be coated therewith and the change in surface tension during the process of coating formation is reduced or decreased to result in prevention of thermal convection and improvement in uniformity of coating film (See Non-patent Document 1: Haruo Kiryu (supervisor), Coating Yo Tenkazai no Saishin Gijutu (Latest Arts of Coating Additives), CMC (2001)). Although the most suitable species of surfactants vary depending on, e.g., the compatibilities with solvent, resin and additives used in the desired coating composition, it is effective to use fluorochemical surfactants in the case of applying a coating with the aid of solvent because of their solubility in solvents and their highest ability to lower surface tension.
In general, a fluorochemical surfactant is a compound having in each of its molecules both a fluoroaliphatic group for performing a function of lowering surface tension and a medium affinity group contributing to affinity for various compositions used for coating or molding materials when the surfactant is used as an additive. Such a compound can be obtained by copolymerizing a monomer having a fluoroaliphatic group and a monomer having a medium affinity group.
Typical examples of a monomer having a medium affinity group, which is polymerized together with a monomer having a fluoroaliphatic group, include poly(oxyalkylene)acrylates and poly(oxyalkylene)methacrylates. On the other hand, there is a report of the antireflective film in which both improvement in airing marks and anti-scratch performance are ensured by use of the fluorocarbon polymer of ω-H type disclosed in Patent Document 2.
However, the use of traditional fluorochemical surfactants can make improvements in drying marks and airing marks, but cannot avoid unevenness of coating and entails a problem of lowering quality of the antireflective film formed through coating.    Patent Document 1: JP-A-7-333404    Patent Document 2: JP-A-2004-331812    Non-patent Document 1: Coating Yo Tenkazai no Saishin Gijutu (Latest Arts of Coating Additives), compiled under supervision by Haruo Kiryu, published by CMC (2001)